It would need a totally different patch, because the WarnOnceAbout infrastructure is not there. So we would be warning on every use, most likely. If that's ok, I can probably write an aurora patch for this....

It means "privileged code", essentially, or "runs with the same privileges as Firefox". I agree that it's somewhat confusing to mention that in the warning, "use an extension" is really the useful advice.

Is there someone other way that I can access UniversalXPConnect without writing an extension? The issue is that I have a website that reads/writes into a log that uses different technologies for each browser (IE, Chrome, Firefox). But removing this functionality, my website won't be able to support Firefox.

Yes, I have the same question. Do you need to access data from the users "private" files, like files from the desktop/Documents/Music/Picutes folders?
Or are you just storing data that you've generated or downloaded from somewhere so that you can retrieve it later?

I am storing log information that is in a format that is generated from my server which generates the client side javascript dynamically depending on the cleint's browers. The data could get large over time (100 MB or more).
The location is in the users' home or documents folder.

Ok, so you are getting the data on your own server and downloading it using javascript (and XHR?). Then you are currently using nsILocalFile to store that data on the users computer and load it back in when needed?
If that is correct, you should soon be able to use IndexedDB to store Blob objects and retrive them as needed. This will work without requiring any extended privileges and simply using web standards!

Jonas, that is correct.
But the issue here is that I want to right to a simple log file (text file) that can be read/written to using any browser. If I use the IndexedDB, it won't be a cross browser solution.
There has to be a better way!

Verfied on:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:7.0) Gecko/20100101 Firefox/7.0
When running a script that uses enablePrivilege I receive the following warning:
"A script from "file://" is requesting enhanced abilities that are UNSAFE and could be used to compromise your machine or data:
Read program settings
Allow these abilities only if you trust this source to be free of viruses or malicious programs."
Then, even if I click on the "Allow" button, the permission those privileges were supposed to grant me is denied.
Is this the correct behavior? If not, please let me know what warning I should get.
Thank you

Verfied fixed on:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:7.0) Gecko/20100101 Firefox/7.0
Steps:
1. Open the Web Console.
2. Open the test case attached in the previous comment.
3. Tap on the "Home Page?" button.
The "Use of enablePrivilege is deprecated. Please use code that runs with the system principal (e.g. an extension) instead." warning is displayed both in the Web console and in the Error console.